Introduction

Our readers already know sound cards on the YMF724 and the YMF744 chips
from Yamaha. The market, however, offers many boards also on the last chip
of the series - the YMF754. One of such boards, AW754 from AOpen (www.aopen.com.tw)
will be considered today. Here, we will touch some issues that were missed
in the previous reviews both on the YMF7x4 chipset series and on sound
cards as a whole.

AOpen AW754

The card we managed to put our hands on was an OEM variant (in a packet
with only a CD).

This is the lightest and cheapest board variant. There is no a digital
optical output though there is a place for it (an optical output can be found only on the AOpen Pro/Deluxe models). In fact, this
board can be completed with a daughter board from AOpen with digital inputs
that connect to S/PDIF in. At least, my board properly worked with all
digital inputs, and there were no any blockages in drivers.

What's interesting inside the YMF754?

The audio chip YMF754
(named DS-1E) is a high efficient audio controller (in terms of
the AC'97 standard) for the PCI bus. The chips consists of two separate
functional blocks - PCI Audio and Legacy Audio (such scheme is typical
for the whole 7X4 series):

The PCI Audio block provides 64 voices polyphony
for the hardware XG wavetable synthesizer (the bank is the same
as in the whole 7x4 series, i.e. appr. 2 MB which can be easily
unpacked up to 6 MB) and effects (reverb, chorus, variation) realized
in drivers. The same block provides DirectSound acceleration.

The Legacy Audio unit supports different additional functions. Such as
a FM synthesizer, Sound Blaster Pro compatibility, support of the MIDI
port (MPU401) and joystick. All these functions are supported in a "clear
DOS", according to Yamaha, theoretically without a need in any drivers.

The YMF754 is designed in a full accordance with the Intel AC'97 standard.
That is, it connects with the AC'97 codecs through the AC-Link bus, and
allows using different variants for board layout - both with one stereo
output and with two (onto the front and rear speakers).

Do not ask us what chip is better at reproduction - the 754 or
724/744, Vortex or EMU10K.

None of these chips can not reproduce music, and influences the reproduction
quality only indirectly (if only chip don't kill quality of sound initially in digits). The matter is that the last three years all new sound chips are separated
from the converters (ADC and DAC) with a digital bus AC-Link:

So, the question on comparison of sound quality, say Live! vs. Vortex2,
in general can be converted into the question: "What sounds better - SigmaTel
or SigmaTel?" :) More competent investigation how different elements of
the digital-analog chain influence the sound quality with precise quantitative
measurements will be considered in my nearest articles.

The 744 and 754 support either one stereo codec or two stereo codecs,
or one 4-channel codec (like on this board). It means that 6-speaker board
on the 7X4 is impossible. By the way, the AC-link frequency due to the
AC'97 standard is fixed at 48 KHz. So, all signals of different frequencies
(22, 32, 44,1 KHz etc.) on the chips output are converted in a single 48
KHz speed. This frequency was set by Intel when developing the specification
with DVD orientation. All AC'97 codecs run at it.

In theory, it doesn't make problems to convert
44.1 to 48 KHz without resampling (according to the experts, such
mode is set in some relatively expensive receiver-transmitters).
It's necessary to put a buffer on the receiving part and to transmit
44.1 with a higher speed, and then in the codec to "assemble" the
signal. But they don't use this scheme in cheap sound cards. Once interpolated
with good mathematics on modern DSP locating in audio-controllers,
and adding pseudo-noise you can reach rather fair results which
should not be audible even on average Hi-Fi acoustics. For seven most
popular frequencies which are derivative from 44.1 and 48 such converting
(SRC - sample rate converting) is earnestly recommended by
the AC'97 to implement hardwarely, on the level of a pair audio
controller/audio codec.

Let's consider the construction of a modern codec and what it allows
connecting inside and outside the computer:

As you can see, all analog out/inputs come to the codec. It means that
it is the codec that first of all determines how the card sounds.

As for digital outputs (both electrical RCA S/PDIF and optical
Toslink), despite the shown Intel scheme, the drop cable usually
goes from an audio controller, i.e. a sound chip. And in this case, the signal goes from the 77-th pin of the
YMF754 to the
place for the connector. Unfortunately, the given board modification doesn't
have such. I tried to solder it myself
(in fact there should be an optical
output), but the SBLive!4830 connected by such a strange way couldn't see
the signal.

That's why it's more reliable to buy a board with a factory
mounted digital output.

Let's, however, come back to our YMF754. Where is it better than its
predecessor in terms of electricity? Like the 744, it supports the IEC958
standard of the digital interface SPDIF. Unlike the YMF744B (DS-1S) chip,
the 754 supports the direct record from the SPDIF In, and at the same time
it doesn't take SPDIF In resources when the Zoomed Video Port is operating.
Besides, Yamaha states a considerable difference in power consumption.
It turned out that the 754 consumes much less energy even at usual operations,
not taking the Standby mode.

The DS-1E supports PC/PCI and D-DMA protocols for DMA emulation in the
style of the SB Pro on the PCI bus. Besides, it supports an old system
of interruptions that use the ISA bus and the Serialized IRQ protocol.
It ensures support for all games in DOS and says that the chips was worked
out 3-4 year ago when it was actual. But as for me, it wouldn't play under
DOS; you'd better do it in Windows, in DOS-window, with a more pleasantly
sounding of the integrated in the card XG MIDI-synthesizer (if you have
a General MIDI option in the game).

Installation and complete utilities

Enough of theory until it is too boring.

Since the card can never be called a Hi-End product, I got prepared
to the fight with drivers, just for case. Surprisingly, none of the driver's part
caused a trouble. And after rebooting, when entering the Windows there
appeared the following screen:

It means that you can immediately check the acoustics connection and card's
working capacity.

he
tray showed me a proprietary AOpen sign, which I want to say some words
on. It's no secret that many companies try to embody something unusual
in their utilities. Well, this was the first utility for the last year
in the tray which I didn't desire to chuck out.

Take, say a standard utility DS-XG Audio Config from Yamaha called
out when choosing the option AW754 Config, accessible also from the Control
Panel (note that the shown picture, for the space to save, is an animated
GIF, for viewing you should enable this option in the browser):

The most interesting is the proprietary utility AOpen AW754 Advanced
Options that contains settings and diagnostics of digital in/outputs
work (here, we also used the animated GIF):

Note a convenient possibility to check whether new drivers were released
with just a double click:

And in case a new driver is found, the utility suggests downloading it
to your computer (selecting the server out of the list):

Shortly, it is a good service for little money.

Testing the sound quality

Now you know that sound quality is determined mainly by the codec and its
analog part on the board (mainly, linear buffers, operational amplifiers
and capacitors). The codec used on the board turned to be our old friend
- the SigmaTel STAC9708.
Well, if they weren't afraid installing this codec in the Aureal SuperQuad
Digital and not so long ago released Creative SBLive! Platinum 5.1, there
is a chance that sound from the codec wouldn't differ much from the more
expensive sound cards. The codec layout is made to be minimum, what carries
both highs and lows.

Below you can see a spectrogram of comparison of the AOpen AW754 and
my reference SBLive! Value 4830 (the Creative CT1297-TAT codec and the
Philips 1330A - front and rear correspondingly). Rewriting of the signal
via the codec's mixer. The 15KHz@-3 dB sinusoid was created in the SoundForge
4.5.

The spectrogram shows that noise floor of the codec of the AOpen AW754
is located very close to that of the Live codec which is in the Digital
Only mode (when adding pseudo-noise to the signal).

I'm not going to make measurements from the linear output to the linear
input, since the input characteristics of the ADC would damage quite a
good DAC. Judging even by the specification, the Signal-to-noise Ratio
(EIAJ CP-307) is: D/A 85 dB A, A/D 75 dB A.

When listening to the AW754 we haven't noticed any artifacts. The board
showed rather decent sounding on the wooden speakers Radiotechnika S-30B
(30 W RMS at 8 Ohm, 50-20000 Hz +-10 dB) and the amplifier ODA-102 (two-piece,
transistor, 10 W). If you have something similar or at least not better
in sounding than the wooden system of the entry level, this card will be
a nice choice for you.

didn't reveal any troubles. Sound nuances of the AW754 from the linear
output were dull and flat like that of the most computer sound cards (the
sound went out simultaneously from the computer and in digital form, for
comparison, at the instant commutation of the signal source from the remote-control
on the receiver). I wish I could have given a digital signal and assessed
the quality of work of the hardware SCR integrated into the 754 chip.

Unlike many top manufacturers, AOpen supplied its product at least with
a evaluation version of the WinDVD (at least, the test sample had
it). The sound track in DVD movies was well decoded by the soft players
WinDVD 2.2 and PowerDVD 3.0. There was nothing to complain about in terms
of sound. But today, I think, it's already time to see 6-speaker solutions
in this price niche.

A bit on game possibilities of the card. As an any normal man, I don't care how many bits
have codecs on the board if it plays mono and makes noise. Or how many
DirectSound streams it supports if the sound is like from a gramophone.
Here, the quality of 3-dimensional sound in games was determined by one
word - Sensaura. If you know it, you'd understand me. The others would
hope that in a cheap solution one can combine all popular 3D interfaces
without performance and quality sacrifice. As for me, I prefer only one
game where the EAX 1.0 via the Sensaura algorithms checks itself perfectly
and outperforms the well-known A3D on the Vortex2, with its unfinished
emulation EAX. The game is Crusaders of Might & Magic (by the way,
made quite dull). In order to enjoy 3-dimensional effects you have to download
a demo from the Internet (it looks like Diablo 1, but in 3D). Those of you who
possess a full version of the game should come to the second or third stage
since only there you might see dynamic actions and only there we could
estimate EAX technology.

Together with this card we received standard demo programs from Yamaha
with wide-known collections of XG MIDI-files. Besides, you can find them
at www.yamaha-xg.com. Once again
I want to summarize XG MIDI sounding in the YMF7x4 based card series. It's
cool for home, for your family (karaoke, DOS-games) and for beginning home musicians.

Conclusion

Despite the fact that I started testing this card without great delight,
the AOpen AW754 surprised me quite pleasantly, and deserved the mark closer
to "must have" than to "must die".

Highs:

The last chip of the 7X4 series from Yamaha

Convenient utilities from AOpen

Not the worst codec STAC9708

Good hardware MIDI for such card

Decent soft on the CD

Lows:

Absence of the digital output (this model)

The Sondius-XG technology works only in Win98

Lack of possibility of any extension with digital outputs

Resume: this product is an excellent budget solution. Maybe, the most universal for such sum.